The glandular kallikreins are a subgroup of serine proteases which are involved in the post-translational processing of specific polypeptide precursors to their biologically active forms. In humans, three members of this family have been identified, and some of their properties characterized (Clements, Endoc. Rev., 10, 343 (1989); Clements, Mol. Cell Endo., 99, 1 (1994); Jones et al., Acta Endoc., 127, 481 (1992)). The hKLK1 gene encodes the tissue kallikrein protein, hK1, the hKLK2 gene encodes the prostate-specific glandular kallikrein protein, hK2, and the hKLK3 gene encodes the prostate-specific antigen protein, hK3 (PSA). Northern blot analysis of mRNA shows that both hK2 and PSA are expressed mainly in the human prostate, while expression of hK1 is found in the pancreas, submandibular gland, kidney, and other nonprostate tissues (Chapdelaine et al., FEBS Lett., 236, 205 (1988); Young et al., Biochem. 31, 818 (1992)).
The nucleotide sequence homology between the exons of hKLK2 and hKLK3 is 80%, whereas the nucleotide sequence homology between the exons of hKLK2 and hKLK1 is 65%. The deduced amino acid sequence homology of hK2 to PSA is 78%, whereas the deduced amino acid sequence homology of hK2 to hK1 is 57%. Moreover, the deduced amino acid sequence of hK2 suggests that hK2 may be a trypsin-like protease, whereas PSA is a chymotrypsin-like protease.
PSA levels are widely used as a prognostic indicator of prostate carcinoma. However, since the concentration of PSA in serum is elevated in patients with either prostatic cancer (pCa) or benign prostatic hyperplasia (BPH), the detection of elevated levels of PSA does not distinguish between these diseases. Moreover, the high degree of homology of hK2 to PSA raises some question as to the specificity of antibodies currently used to detect the levels of PSA. If the levels of circulating hK2 are unrelated to pCa or BPH, then antibodies raised to preparations of PSA which are contaminated with hK2, or to regions of PSA with homology hK2, can result in false positive results. However, determination of the levels of hK2 in serum, and the correlation of those levels in patients with pCa or BPH, have not been accomplished.
Thus, a need exists for a method to isolate and purify hK2 polypeptides for use as therapeutic and/or diagnostic agents.